Steering column of a motor vehicle

ABSTRACT

A gas compression spring (10), is built into the telescoping shaft (1, 2) of a steering shaft. Via a cap element (12), the gas compression spring (10) presses against an articulated fork (6) and the piston rod (11) of the gas compression spring (10) presses against a lower articulated fork (7). The gas compression spring (10) and the piston rod (11) are accommodated in a stepped bore (8) of a sliding part (2) of the steering shaft of the telescoping shaft.

BACKGROUND OF THE INVENTION

The invention relates to an axially adjustable steering column for motorvehicles, whose steering shaft has parts that telescope inside oneanother, such as a steering shaft tube and a sliding part of thesteering shaft, which to attain play-free engagement are loaded againstone another in the circumferential direction.

DESCRIPTION OF THE PRIOR ART

From German Patent Application DE 40 34 819 A1, a steering column formotor vehicles is known which has an integrated hydraulic cylinder thatcan be actuated in the axial direction. The hydraulic height adjustmentby means of the pressure chambers is done with the aid of solenoidvalves, a pressure limiting valve and a check valve. A pump alreadypresent for the onboard hydraulic system can be used as a source ofpressure medium. This kind of steering system includes a relativelylarge number of additional parts and takes up a large amount ofstructural space.

When the clamping device of an adjustable steering column is undone, thesteering wheel drops to its lowermost adjusted position, both by its ownweight and the weight of the adjustable parts of the steering column. Inan extreme case, the weight of the steering wheel and of the upper partsof the steering column can be as much as 30 kg. The driver on adjustingthe position of the steering wheel must therefore overcome by force,this weight, in order to put the steering wheel into the desiredposition. This can be done only by exerting great force.

To absorb the force of this weight, a compression spring is thereforebuilt in between the displaceable parts of the telescoping shaft. Thetelescoping shaft is the connection between the steering wheel and theupper steering column. Because of the strong forces and the relativelysmall structural space available, the compression spring has a highspring constant and thus creates a major force increase over theadjusting range.

Thus, the force of the weight cannot be compensated for over the entirestroke length range. Because of the restricted structural spaceavailable, the compression spring can be accommodated only on the outerdiameter of the telescoping shaft, which has the disadvantage ofconsiderably increasing this outer diameter. The stroke lengthlimitation, that is, the end stop for the compression spring, must beaccomplished by the telescoping shaft. Given the strong spring forces,the result can be damage to the ball guide of the telescoping shaft.

SUMMARY OF THE INVENTION

The object of the invention is to relieve the driver of this high forceof the weight as he adjusts the position of the steering wheel. Thissolution should not take up any additional structural space.

According to the invention, this object is attained by a gas compressionspring built into the upper portion of the sliding part of the steeringshaft which is braced via a piston rod against a structural componentconnected to the steering shaft tube. The spring constant of the gascompression spring can be designed in such a way that the change inforce over the stroke length range is minimal; that is, the force thatcounteracts the force of the weight varies only insignificantly over theaforementioned adjustment range of the steering column. When theclamping device of the steering column is undone, the steering wheel"floats" in its position. In contrast to known steering systems, noadditional structural space is needed for the gas compression spring.The gas compression spring has its own stroke length limitation, so thatno destructive forces act upon the telescoping shaft.

In a further feature of the invention, the sliding part of the steeringshaft has a stepped bore for receiving the gas compression spring, andthis bore is closed off by a cap element. The piston rod extends throughthe reduced-diameter portion of the stepped bore and is braced on anarticulated fork connected to the steering shaft tube.

It is expedient to provide a ball guide, comprising longitudinal groovesand balls, between the steering shaft tube and the sliding part of thesteering shaft, which guide can compensate for the relative motionsbetween the driver's cabin and the chassis of the vehicle.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional view of a steering column of a motor vehiclein accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A steering shaft tube 1 and a sliding part 2 of the steering shaft of atelescoping shaft have longitudinal grooves 3 and 4 on the inner andouter diameter, respectively. Balls 5 are inserted between theselongitudinal grooves to provide low-friction displacement. The upper endof the sliding part 2 of the steering shaft has an articulated fork 6 ofa cross joint 6A, and the lower end of the steering shaft tube 1 has anarticulated fork 7 of a cross joint 7A. The sliding part 2 of thesteering shaft has a stepped bore 8, in which a gas compression spring10 is integrated, the gas compression spring comprising a piston 10Awith a passage 10B therethrough and a piston rod 11. Pressure chambersabove and below the piston 10A are filled with gas in a manner known perse.

The stepped bore 8 is closed off on the upper end by a cap element 12.The end of the gas compression spring 10 is braced on this cap element12 against the sliding part 2 of the steering shaft. A seal 13 islocated on the lower end. The piston rod 11 is braced on the articulatedfork 7, so that the steering shaft tube 1 and the sliding part 2 of thesteering shaft are forced apart by the gas compression spring 10. Thepiston 10A is shown in the built-in position. A stroke H1 to the top anda stroke H2 to the bottom are available. The strokes H1 and H2 dictatethe possible range of adjustment. The balls 5, which are guided in acage 5A, allow rolling friction upward as far as a stop ring 14 anddownward as far as a stop ring 15. Sliding friction takes place as well.Within the rolling friction, the relative motions between the driver'scabin and the chassis can be compensated.

We claim:
 1. A combination of an axially adjustable steering column anda steering wheel of a motor vehicle comprising:a steering shaftincluding a lower steering shaft tube and an upper sliding part to whichthe steering wheel is connected, said steering shaft tube and saidsliding part telescoping inside one another, and said steering shaftfurther including a bearing mechanism which loads said steering shafttube and said sliding part against one another in a circumferentialdirection to attain a play-free telescoping engagement whereby saidupper sliding part and the attached steering wheel together exert acombined downward weight relative to said steering shaft tube; astructural component connected to said steering shaft tube; and aself-contained gas compression spring built into said sliding part andincluding a piston, two pressure chambers separated by said piston, aflow path between said pressure chambers providing flow between saidchambers at all times and lacking any flow cutoff valve therefor, and apiston rod extending from said piston and braced against said structuralcomponent, said gas compression spring solely compensating forsubstantially the combined downward weight of said sliding part and thesteering wheel connected thereto relative to said steering shaft tube atall times such that said sliding part and the steering wheel connectedthereto float weightless relative to said steering shaft tube at alltimes and such that said sliding part and said steering shaft tube arefreely adjustable relative to one another free of the combined weight.2. A combination of an axially adjustable steering column and a steeringwheel as claimed in claim 1:wherein said sliding part of said steeringshaft has a stepped bore having a reduced portion and a cap elementwhich closes off said stepped bore, said stepped bore receiving said gascompression spring; wherein said piston rod extends through the reducedportion of said stepped bore; and wherein said structural component isan articulated fork connected to said steering shaft tube.
 3. Acombination of an axially adjustable steering column and a steeringwheel as claimed in claim 2;wherein said bearing mechanism is a ballguide having longitudinal grooves and balls provided between saidsteering shaft tube and said sliding part.
 4. A combination of anaxially adjustable steering column and a steering wheel as claimed inclaim 1;wherein said bearing mechanism is a ball guide havinglongitudinal grooves and balls provided between said steering shaft tubeand said sliding part.